Conformational diseases are neurodegenerative maladies in which the accumulation of amyloid-like fibrillar forms of aberrantly folded proteins cause dementia and cell death via unknown mechanisms. Hsp40s are molecular chaperones that direct Hsp70 to interact with disease related proteins and partition them between pathways for folding, aggregation and amyloid formation. Prions are infectious proteins that that assemble into a self-perpetuating amyloid-like state that is associated with neurodegeneration. The study of yeast prions has provided many of the basic details about chaperone function in amyloid fibril formation. In preliminary studies we developed a number of assays to monitor Hsp40 action in modulating amyloid formation and toxicity. The studies proposed herein are designed to define mechanisms by which aberrant prion biogenesis causes cell death. In addition, we seek to identify the specific steps in prion assembly that are catalyzed by different Hsp40s. Finally, we will determine the structure and functional features of Type I and II Hsp40 sub-types that specify their action in prion biogenesis. The data obtained from these studies will define the rules for Hsp40 function in amyloid formation and identify therapeutic targets for the treatment of conformational disease. Conformational diseases are a neurodegenerative maladies in which the accumulation of amyloid-like fibrillar forms of aberrantly folded proteins cause deimentia and cell death via unknown mechanisms. The data obtained from the proposed studies will define the rules for Hsp40 function in modulation of amyloid formation and toxicity and identify therapeutic targets for the treatment of conformational disease.